On Wed, 2011-05-18 at 09:35 -0600, Moore, Eric wrote:

I worked the original defect a couple months ago, and Kashyap is now
getting around to posting my patch's.

This original defect has nothing to do with PPC64.  The original
problem was only on x86.    It only became a problem on PPC64 when I
tried to fix the original x86 issue by copying the writeq code from
the linux headers, then it broke PPC64.   I doubt that broken patch
was ever posted. Anyways, back to the original defect.  The reason it
because a problem for x86 is because the kernel headers had a
implementation of writeq in the arch/x86 headers, which means our
internal implementation of writeq is not being used.  The writeq
implementation in the kernel is total wrong for arch/x86 because it
doesn't not have spin locks, and if two processor simultaneously doing
two separate 32bit pci writes, then what is received by controller
firmware is out of order.   This change occurs between Red Hat RHEL5
and RHEL6.  In RHEL5, this writeq was not implemented in arch/x86
headers, and our driver internal implementation of write was used.

You may also want to look at Milton's comments, it looks like the way
you do init_completion followed immediately by wait_completion is racy.

You should init the completion before you do the IO that will eventually
trigger complete() to be called.

Cheers,
Ben.